I tried to vote to close Einstein problem; on mirror symmemtry as a duplicate of Aperiodic monotile without reflections?. But the software gave me an error I wasn’t expecting: it said because the earlier question did not have an answer with a positive score, I could not vote to close as a duplicate. Is this the intended functionality? I would think that we should close duplicate questions, even when they are duplicates of questions that are unanswered.


2 Answers 2


I will quote from the help center - the part about duplicates:

In general, the original question must have an answer; questions may only be marked as duplicates of unanswered questions (a) on meta sites, (b) when the questions share the same author, or (c) when closed by a moderator.

And here is a quote from the FAQ post "How does duplicate closing work? When is a question a duplicate, and how should duplicate questions be handled?" (current revision)

Unanswered duplicates: Generally, a question cannot be closed as a duplicate of a question with no upvoted or accepted answers, unless:

  • the site is a meta site
  • the questions were posted by the same user
  • a moderator closes the question

On main sites, the main point of closing questions as duplicates is to point users to better answers; closing a question as a duplicate of an unanswered question defeats this purpose. Also, this reduces the risk that question A is closed as a duplicate of question B even though the particular circumstances of question A allow an answer that wouldn't work for B. If you're convinced that two unanswered questions are duplicates, flag one for moderator attention and explain your reasoning.

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    $\begingroup$ Okay, thanks, I see that this is intended functionality. $\endgroup$ Commented Mar 30, 2023 at 20:53
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    $\begingroup$ It would be nice to find whether introducing this functionality was discussed at some point. I searched a bit and did not find such discussion - maybe someone else might have more luck. $\endgroup$ Commented Mar 30, 2023 at 20:57

This is just me recording my thoughts as to why, for MathOverflow, voting to close a question as a duplicate of an unanswered question should be an option. MathOverflow is a bit different from other question & answer stack exchange sites. For other sites, helping people quickly find answers is the main goal, and so it makes sense to only close a question when you can point them to an answer. But, while answering questions is of course also an important goal on MO, I would say there are other goals as well. The participants in MO are potentially engaging in math research. One important aspect of academic research is acknowledging priority. Moreover, in math, questions themselves are valued as contributions. So, at a minimum, it is important to acknowledge priority in question-asking.

I also see MathOverflow as a repository of mathematics knowledge. Over time, the database of both questions and answers grows, and people who want to learn can search (either on MathOverflow itself or e.g. via Google) to find that a question they have may have already been asked and/or answered. To keep this database "clean" and "useful," getting rid of duplicate entries (for both questions and answers) is a good idea.

Finally, let me say that I don't think every duplicate question needs to be closed as a duplicate. I wish I had the specific example on hand, but I remember recently reading a question where the asker acknowledged that it was a duplicate of an old (maybe ~10 years old), unanswered MO question. They wanted to re-ask the question in case there have been any updates in the field which may have lead to it being answerable now even though it wasn't before. I think this is totally fine, especially when you acknowledge the previous question. But for example on the other hand, the question I linked above was a duplicate of a question that was asked only a week ago, so it definitely was not contributing anything new to MO.


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